1. Field of the Invention
The present invention relates to a method and apparatus for determining the contents of salt and water in a water-in-oil type emulsified product (which is a preparation comprised of an aqueous solution dispersed in a fat or oil). The water-in-oil type emulsified product includes a butter, a margarine and other spreads.
2. Description of the Prior Art
Salt and water contained in the water-in-oil type emulsified product are important components which decide the quality of the water-in-oil type emulsified product, and the examination of the dispersed state of the salt is also an item which is important for a quality control. Therefore, in order to control the contents of salt and water or the dispersed state of the salt, the determination of the contents of salt and water is frequently carried out in a manufacturing process.
The methods for determining the content of salt which have been conventionally used are (1) a method (Mohr's method) which comprises extracting a sample with water and titrating the extracted solution with a normal solution of silver nitrate, (2) a determining method which comprises extracting salt from a sample with water and measuring the content of salt in the extract by mean of a sodium ion meter or a chlorine ion meter, and (3) a method for measuring the content of salt by mean of .gamma. ray absorption technique. The methods for determining the content of water which have been conventionally used include (4) a drying method in content, (5) Karl Fischer method, (6) a method using a dielectric constant, and (7) a microwave absorption method.
However, the above prior art methods for determining the contents of salt or water contain several problems. Those are, as the methods for determining the salt content, the method (1) has complicated processes such as the extraction and the titration, and is time consuming, so it is not suitable for on-line analysis, the method (2) has the problem of a need for an extracting process, the problem of the accuracy of the ion meters and the problem of the contamination of the electrode with oil and the method (3) has the problems of safety handling, and food protection radiation. As the methods for determining the water content, the method (4) is an official and basic method specified in "Ministerial Ordinance relative to Specification or the like of Components of Milk and Milky Product", Japanese Welfare Ministry Ordinance No. 52, Dec. 27, 1951, but has problems that the measurement is of a batch type and time consuming and it is not suitable for on-line analysis. The method (5) is complicated in operation and high in analysis cost. In the method (6), when salts are dissolved in a water phase of an emulsified product, the salts content influences the dielectric constant, a water content cannot be obtained from dielectric constant alone. Thus, the water content cannot be determined with dielectric constant as a result of disturbance of salts.
In this way, the prior art methods are unsuitable for rapid and accurate determination of salt and water content.
Accordingly, the present inventors have made a search for rapid measureable physical quantities (measureable items from which salt and water content can be calculated. However, the suitable items cannot be found among known physical properties. Accordingly, the present inventors had made studies for methods for determining salt and water content by use of a plurality of measureable items which are not correlated to one another, and consequently have found that the intended purpose can be achieved by using a dielectric constant (or a relative dielectric constant or a microwave absorption index) and a specific gravity together.
More specifically, the present invention could be accomplished by finding the following respects (a) and (b):
(a) If the specific gravities and relative dielectric constants of components (i.e., salt and water) of a water-in-oil type emulsified product have specific value, are constant, the specific gravity and relative dielectric constant of the entire water-in-oil type emulsified product (i.e., two physical quantities of the water-in-oil type emulsified product) can be determined according to proportions of the individual components.
(b) Salt and water content the water-in-oil type emulsified product can be determined as criterion variables, if two physical quantities (e.g., a specific gravity and a relative dielectric constant) are used as explanatory variables.
The above (a) and (b) will be described using a margarine, as an example, which is a water-in-oil type emulsified product.
As described in "Solution Chemistry", pp. 116, Hitoshi Otaki (issued from Shoukabou, Sep. 30, 1985), a decrement in specific dielectric constant is represented by the following expression formula (1): EQU C(.delta..sub.+ +.delta..sub.-) (1)
wherein C represents a content of an electrolyte, and .delta..sub.+ +.delta..sub.- represent effects by a cation and an anion, respectively.
The components of a margarine which is a water-in-oil type emulsified product and the characteristic values of the components will be defined as given in Table 1.
TABLE 1 ______________________________________ Component Composition (%) S.G. R.D.C. ______________________________________ Fatty oil 100-M-N G.sub.1 C.sub.1 Water M G.sub.2 C.sub.2 Salt N -- -- ______________________________________ S.G. = Specific gravity R.D.C. = Relative dielectric constant
With a definition as given in Table 1, the specific gravity of the entire solution of salt contained in the margarine is represented approximately within a given range of variations by the following expression formula (2): EQU G.sub.2 +[k.multidot.N/(M+N)] (2)
wherein k is an experience value and is a constant within such given range of variations.
Therefore, if the specific gravity of the entire margarine is represented by B, the value of B can be represented by the following expression formula (3): EQU B=G.sub.1 .times.(100-M-N)/100+[G.sub.2 +kN/(M+N)].times.(M+N)/100(3)
On the other hand, the relative dielectric constant of the entire solution of salt contained in the margarine is represented by the following expression formula (4) in the same manner as with the expression formula (1): EQU C.sub.2 -(.delta..sub.+ +.delta..sub.-)N/(M+N) (4)
wherein .delta..sub.+ and .delta..sub.- are reduction effect coefficients of relative dielectric constants of Na.sup.+ and Cl.sup.- and are values found experimetally, respectively.
Because the solution of salt and the fatty oil are in a simple mixed state and the actually measurable range is narrow, an addability can be established. Therefore, the relative dielectric constant of the entire margarine is represented by the following expression formula (5): EQU A=C.sub.1 .times.(100-M-N)/100+[C.sub.2 -(.delta..sub.+ +.delta..sub.-)N].times.(N+M)/100 (5)
By solving the above expressions (4) and (5) for M and N, the following expressions formulas (6) and (7) are provided: ##EQU1##
The above expressions (6) and (7) indicate that the contents N and M of salt N and water M in the margarine (i.e., the water-in-oil type emulsified product) can be determined as objective variables (dependent variables), when the specific gravity and the relative dielectric constant of the water-in-oil type emulsified product are used as explanatory variables (independent variables).
It can be seen from the above description that if a bivariable multiple regression equation is employed, wherein the specific gravity and relative dielectric constant of the water-in-oil type emulsified product are used as explanatory variables, and the contents of salt and water in the water-in-oil type emulsified product are used as objective variables, the objective variables (the contents of salt and water) can be found. It can be also seen that the contents of salt and water can be found by employing the dielectric constant and specific gravity, or the microwave absorption index and specific gravity as two explanatory variables (i.e., two measureable physical quantities) according to a theory substantially similar to that described above.